The present invention concerns a device for measuring the level of liquid fuel in a tank of the type known under the name "sabre", that is, in which one marks the void space between the surface of the liquid and a reference plane near an opening that gives access to the tank. Generally, two pins are provided against which one rests two similar support surfaces that are integral with the apparatus and which thus determine the degree of penetration of the latter into the tank.
These devices are generally made in the form of a long dipstick carrying marks or graduations that serve as references to determine the wet height, representing the actual level of liquid fuel in the tank.
French patent no. FA-A-2,560,678, published Sept. 6, 1985 in the name of the applicant also describes a refinement to this type of device in which one amplifies the variations of liquid level to increase the accuracy and resolution of the measurement. This document also indicates the special application of devices of this type in surveillance of proper sampling of meters that measure the amount of liquid delivered from the tank, verification that requires good accuracy of level measurement.
One of the purposes of the invention is to increase the accuracy and resolution of these devices, while preserving a device that is easy to use, simple in design and autonomous in function. As regards the last condition, one will recall that measurement of the fuel level is made in an explosive atmosphere which precludes electrical proceses involving switches, capacitive, piezoelectric sensors, positioned in situ and connected to a remote measurement device.
One will see that the device of the invention permits measurement accuracy of about .+-.0.5 mm and a resolution (smaller detectable variation) of about 0.05 mm. These figures should be compared with the accuracy and resolution of a conventional "sabre", which are both about 1 mm, these figures corresponding to the accuracy of interpretation of the wet height on the graduated part of the sabre.